Bottom watering reduces water stress and disease pressure, while also encouraging healthier roots
There’s a revolutionary way to water, and not enough people know about it. Most of us (myself included) probably overhead water our plants. It’s easy and fast, and it’s the way we see most professionals water. But it’s not the only way—and maybe not even the best way—to irrigate.
Bottom watering is an irrigation method that allows plants to absorb water from their base rather than from the surface soil. This way of watering is proven to be much healthier for seedlings and mature plants since it promotes healthier root development. Bottom watering all but eliminates water stress and the soilborne diseases associated with overwatering.
Keep reading to understand how bottom watering works, why you should make the switch to this irrigation method, and how to bottom water your plants at home!
The science behind bottom watering
Bottom watering works through a process called capillary action. Soil particles in contact with water particles wick the moisture up through the soil until the water can be picked up by plant roots.
Water is adhesive – meaning, water adheres to itself and to almost everything else (you’ve probably noticed this). That’s why capillary action works so well to pull water from the bottom of the pot to the plant roots.
And once plant roots pick up the water particles, they continue to pull the moisture where it needs to go. The United States Geographical Survey has a great article explaining how water moves against gravity.
Bottom watering is good for all plants: annual vegetables, perennial flowers, houseplants, and everything in between.
The benefits of bottom watering
Why bother with bottom watering? Bottom watering is much better for plants than top watering because of these seven reasons:
1. Even and consistent moisture
Bottom watering controls the amount of water that reaches plant roots by only allowing a volume that the root system can take. It’s much harder to overwater plants with bottom watering because the plants only absorb as much water as they need.
This method of watering is especially beneficial for underwatered plants. Instead of the onslaught of water typical to top watering, bottom watering allows dry roots to absorb water slowly and evenly, without shocking a thirsty plant.
Perhaps the greatest benefit of bottom watering is getting on an even and consistent watering schedule, which will drastically reduce the amount of stress on plants.
2. Conservation of water
Top watering is notorious for water waste. Bottom watering, however, forces us to use less water over a shorter timeframe.
When we water from above, the exposed parts of the soil quickly lose moisture through evaporation. Watering from the bottom not only saves water, but the plants are able to hold that moisture longer, since it is less likely to evaporate.
(In case of drought, you can learn more about how to garden without water here.)
3. Reduces soil compaction
When you water from the surface, the weight of the water can result in soil compaction. Watering from the bottom is a much gentler irrigation method that doesn’t change the composition or the consistency of the soil over time.
4. Eliminates backsplash
Some plants—like tomatoes—don’t like for their foliage to get wet. Bottom watering is perfect for those plants that prefer to keep their leaves dry, since the foliage doesn’t come into contact with moisture at all.
Backsplash, or the water droplets that adhere to plant leaves as a result of top watering, can lead to fungal diseases if plant foliage stays wet.
(Pruning the bottom leaves of tomatoes can help to prevent disease – you can learn more here).
5. Less disease
Damping off (a fungal disease that results from stagnant air, excess moisture, and unsanitized pots and seed trays) can be a huge problem for many growers. Damping off shows itself in seedlings that develop weak stems and topple over, seemingly overnight.
Diseases like damping off, root rot can be easily prevented through bottom watering. Watering from the bottom prevents water from sitting on the topsoil, which can lead to root rot and other fungal diseases.
This is particularly important for potted plants, as it prevents fungal diseases from becoming established in the surface soil.
Seedling trays that are bottom watered are far less likely to develop green mold and algae than top-watered trays. While green mold isn’t a major problem in and of itself, it does signal the greater underlying issue of overwatering.
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6. Fewer pests
Overwatering weakens plants’ immunity, so it’s much better to err on the side of caution and bottom water pest-prone plants. Since bottom watering doesn’t always reach the surface soil, pests like fungus gnats are less likely to take up residence in your plant pots.
Once you have pests, it’s hard to eradicate them completely. Bottom watering won’t simply solve an existing pest problem, but if you bottom water from the beginning your plants are less likely to develop pests in the first place.
When you water from the top, you risk spreading mold, mildew, or pests from one leaf to another. Bottom watering keeps the aforementioned risks away from your plants.
7. Healthy root development
Air needs to reach the root zone of the plant in order to keep them strong and healthy. When the soil on top of the root zone is overly saturated, it can create poor soil aeration, making it very difficult for the roots to breathe. Bottom watering ensures the roots will get the oxygen it needs to promote healthy root development.
Watering plants from the bottom also encourages deeper root growth — and deeper roots mean more access to nutrients and water, as well as provide a stronger anchor for top-heavy plants.
Plant roots are forced to stretch down and out to absorb water and nutrients, rather than collect moisture from the surface soil. The result is well-developed root systems that are far more likely to survive transplanting and periods of drought.
Drawbacks of bottom watering
There’s hardly an argument against bottom watering, but it can be more of an inconvenience than other types of irrigation. Bottom watering may require you to move plants around, and particularly big pots may be uncomfortable to move.
Bottom watering only works for plants that are already in containers, like potted plants and seedlings. It’s impossible to bottom water in-ground crops, although installing drip irrigation is an excellent option.
Watering from the bottom may also cause some minerals and salts to build up in plant pots, especially if you use tap water. You can counter this buildup by using purified water, or you can periodically flush plant pots by overhead watering until water is freely flowering out the bottom of the pot.
How to bottom water plants the right way
Bottom watering isn’t difficult or expensive–it just takes time and some diligence. You can’t mess it up – unless you forget to dump the excess water!
- First, check the soil to decide if your plants even need to be watered. The best way to check for moisture is to lift up the bottom of a plant pot or seedling tray and check to see if the soil is dry. If it is, it’s time to water. If the soil is still fairly wet, hold off on watering and check back tomorrow.
- Now, gather the bottom trays. I like to use watertight germination trays because they nest nicely underneath seedling trays and four-inch pots, but you can use other containers, too — even your kitchen sink, bathtub, or a plastic bin or metal feeding trough. Anything that will hold water and is big enough to accommodate your plant pots is perfect.
- Next, fill the container with a couple of inches of fresh water. Large pots and plants may need more than a few inches of water, but one or two inches is ideal for seedlings and small pots.
- Nest the seedling tray in the bottom tray, or place pots in the container.
- Allow the plants to sit in the water for at least 10 minutes, but no more than 30. Check on the plants every 10 minutes or so. When the surface soil is wet, the plants are fully saturated and can be removed. If the pots absorb all of the water but are still dry to the touch, add a little more water.
- After your plants are fully hydrated or after 30 minutes (whichever comes first), remove the plants from the bottom tray and dump the excess water. You can return the pots or seedling flats to their bottom tray if you wish, as long as the bottom tray is empty.
Some additional tips
- Bottom watering is best for small to medium-sized containers, since moving the containers is required. Make sure you use containers that have holes in the bottom, or the water can’t be wicked up!
- How often you should bottom water depends on a lot of external factors, like how much sun your plants get or how hot it is outside. You’ll probably find that you need to bottom water every three to four days—but always check the plants before watering them, as changing temperatures and humidity levels might mean that the plants need to be watered sooner or even later than expected.
- Although liquid fertilizer is usually applied to plants via overheard watering, you can certainly fertilize seedlings and plants through bottom watering. Simply dilute the fertilizer per the manufacturers’ instructions and pour the solution into the bottom tray. As usual, dump the excess water after a half hour.
Different ways to bottom water
Now that you have a general idea of how to bottom water, here are a few fun variations.
·Use a capillary mat
A capillary mat works similarly to a watertight bottom tray, but with a greater ability to wick water up. Capillary mats are effective at the commercial level, but home gardeners can use them at home. Commercial capillary mats are made of polypropylene but you can even make your own of felt or another sponge-like material.
Capillary mats need to be used with a drip tape system to supply the water. You’ll want to lay down drip tape before placing the capillary mat on top of a table or other elevated surface.
To use a capillary mat, simply lay the mat down on a table or the ground and place your plants on top of the mat. Fill the mat with water until it reaches the bottom of your trays.
·Use a plant mister
If your plant container has holes in the bottom (or you are growing in a porous substance like coco coir or a rockwool cube), you can use a plant mister to water from the bottom. Just fill the mister with water and mist the soil from the bottom.
This method works well for small containers, but it is most effective if you mist several times in succession to make sure the soil absorbs enough water.
·Use a wicking system
This is the most advanced way of bottom watering, and requires some setup and tinkering. A wicking system is exactly as it sounds: a system of wicks that pull water up from a reservoir and wick it into the soil.
This system is great for containers, hydroponic gardens, and larger hydroponic setups. The reservoir can be as small or as large as you like, and the wicking material can be anything from rope to fabric, although the material should be absorbent and non-toxic.
·Use a self-watering container
If you’re growing in unglazed ceramic pots, you can use self-watering containers. These have a water reservoir at the bottom that is filled with water, and a water gauge in the side, so you can see how much water is in the pot.
The pot will slowly absorb the water into the soil, keeping the plants nourished and hydrated.
(You can learn much more about self-watering gardens here).
Bottom watering is a great way to save time and water, and it results in healthy, thriving plants. Used carefully and with the proper supplies, bottom watering can save you time, water, and energy, resulting in healthy plants all around.
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About the author:
When not writing content or growing flowers in her native Virginia, you can find Sarah hiking a long-distance trail deep in the woods. Follow along with Sarah’s adventures at http://sarahcolliecreative.com.